Polyodontosaurus

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Polyodontosaurus
Temporal range:
Ma
↓
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: †Troodontidae
Genus: †Polyodontosaurus
Gilmore, 1932
Species:
†P. grandis
Binomial name
†Polyodontosaurus grandis
Gilmore, 1932
Synonyms
  • Polydontosaurus van der Reest &
    Currie, 2017 (sic
    )

Polyodontosaurus (meaning "many-toothed lizard") is a potentially dubious

troodontid dinosaur named in 1932 by Charles W. Gilmore for a left dentary from the Dinosaur Park Formation.[1] It had been considered a synonym of Stenonychosaurus or Troodon for a significant time, before being declared a nomen dubium
. The only known species is the type, P. grandis.

History of discovery

The

dentary, lacking any teeth. Sternberg presented the dentary to Charles Gilmore, who identified it as a lizard. Gilmore thus named the binomial Polyodontosaurus grandis for the new taxon in 1932.[1] Sternberg revisited the material in 1951 and determined that it represented a carnivorous dinosaur based on the general morphology of the bone, as well as the anatomy of the Meckelian groove, multiple nutrient foramina, and separation of teeth into multiple sockets. Sternberg compared this dentary to one referred to Troodon by Russel in 1948, and decided that they belonged to the same family, and potentially the same genus. While similar, there were a few differences, that might be shown to relate to age or variation within the genus. Sternberg, therefore, referred Polyodontosaurus to the family Troodontidae, until further material could be found.[2] The name Polyodontosaurus has been misspelled as "Polydontosaurus" by some authors.[3]

Polyodontosaurus, represented by the holotype CMN 8540, was found in the Steveville area in the Dinosaur Park Formation. It was found about 37 m (121 ft) below the highest layer of the formation, and comes from the MAZ (Megaherbivore assemblage zone)-2 portion of the fauna, which existed after MAZ-1. This exact stratigraphic location cannot be verified. MAZ-2 spans from 75.9 to 75.3 million years ago, CMN 8540 is from slightly above (younger) than the middle of the formation.[3]

In 1969 Dale Russell described a new specimen of Stenonychosaurus, a troodontid closely related to Saurornithoides. This specimen, CMN 12340, was from the Oldman Formation of Alberta, which lies directly above the Dinosaur Park Formation.[4] This specimen was later named Latenivenatrix and comes from the MAZ-2 level of the formation.[3] Because of the similarities between Polyodontosaurus, Stenonychosaurus, and more complete Saurornithoides, Russell concluded that Polyodontosaurus was a junior synonym of Stenonychosaurus, and that they both might be synonyms of the tooth-taxon Troodon, although the material of Troodon is very incomplete.[4]

Classification

After being initially named as a lizard, Polydontosaurus was reclassified as a troodontid, a classification which stands today.[2][3] Since 1969 Polyodontosaurus has been considered a synonym of Stenonychosaurus, and later its senior synonym Troodon.[4][3] Polyodontosaurus is potentially a synonym of the taxon Latenivenatrix, named in 2017, but they may come from separate regions of the formation. Van der Reest & Currie in 2017 determined that due to the lack of sufficient material in the holotype, and that the dentaries of troodontids to not bear unique, autapomorphic features, Polyodontosaurus was a nomen dubium, and could not be considered senior synonym of Latenivenatrix.[3]

Below is the phylogenetic analysis of van der Reest & Currie (2017). Polyodontosaurus has been considered a synonym of the "Two Medicine troodontid" and Latenivenatrix previously.[3]

Troodontidae

Paleoecology

Megafaunal dinosaurs of the Dinosaur Park Formation

The single specimen of Polyodontosaurus was found in the central level of the Dinosaur Park Formation, and was a member of a diverse and well-documented

angiosperms.[7]

References

  1. ^
    Belly River Formation
    of Alberta. Transactions of the Royal Society of Canada, section 4, series 3 16:117-119
  2. ^ a b Sternberg, C.M. (1951). "The lizard Chamops from the Wapiti Formation of Northern Alberta: Polyodontosaurus grandis is not a lizard". Annual Report of the National Museum of Canada Bulletin. 123: 256–258.
  3. ^
    hdl:1807/78296
    .
  4. ^
    doi:10.1139/e69-059
    .
  5. ISBN 978-0-520-24209-8
    .
  6. ISBN 978-0-253-34595-0
    .
  7. ISBN 978-0-253-34595-0
    .
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